| This thesis focuses on the simulation of organic light-emitting diodes (OLEDs) and organic photovoltaic devices (OPV). By building the model and choosing appropriate parameters, I reproduced the experimental data collected by my colleagues and interpreted the results qualitative and quantitatively.;We begin by simulating single layer devices to establish a good understanding of the charge carrier injection, transport and recombination. Efficiency of single layer OLEDs is sensitive to the mobilities of electrons and holes. Charge carrier traps can be introduced to balance the transport. We then systematically investigate the effect of the layer structure on the current efficiency in bilayer and trilayer OLEDs, and conclude that inserting a hole injection layer can effectively reduce the quenching by charge carriers near the recombination zone and hence improve the current efficiency. Mixed host OLEDs with different device structures have been simulated and compared.;We next investigate the effect of the highest occupied molecular orbital (HOMO) energy level offset on planar heterojunction OPV devices, where dissociation at the donor/acceptor (DA) interface controls the device performance. Bound charge-transfer (CT) states are produced when excitons arrive at the DA interface. The following dissociation of CT states is simulated using the Braun-Onsager model. Two fitting parameters, the initial separation distance r0 and the CT state decay rate kf, are used to explain the effect of the HOMO offset. The S-shape current-voltage characteristics and the donor layer thickness dependence of the device performance are explained by the hole transport limitation in the donor layer.;For bulk heterojunction (BHJ) OPV devices that mix the donor and acceptor materials in the BHJ layer, the device performance is sensitive to the donor concentration. We explained this finding by considering the donor concentration dependence of parameters in the BHJ layer, including the absorption coefficient, dielectric constant, and hole/electron mobilies. A good match between the simulation and experimental results has been achieved when all the parameters are set properly.;Finally, we simulate the two-stack tandem OPV devices and predict the optimal combination of the BHJ layer thickness for both subcells, which is confirmed by experiments. |
